Lots of stuff to do there as Kang pointed out. If you have a morning and afternoon to kill to do the wall go to the more remote sections and avoid BadaLing, too many tourists and it is pretty much all restored. MuTianYu (i think) is the more remote section, ask the hotel.
Oh and go muck around the old HuTongs, all sorts of neat stuff to see if you do not want to go too far out of town and have an afternoon to spare.
If you have not done the Forbidden City, Summer Palace and Temple of heaven then those should take up a day. The Temple of Heaven was under scaffolding several months ago when i was there.
I plan to go look up this dude next time in Beijing. If you are into Archery...
http://www.chinaculture.org/gb/en_artqa/2006-02/14/content_79283_3.htm
Enjoy, take lots of pics.